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1. Space Environment
Lecture 32 – Space Debris (Vol. 3)
Large constellations (part 1)
Professor Hugh Lewis
SESA3038 Space Environment

2. Overview of lecture 32
• In this lecture we look back (very briefly) to remind ourselves why
constellations of satellites in LEO are useful and why they might present
problems for the space environment, before we focus on a simulation study
conducted for ESA:
– Aiming to understand the sensitivity of the debris environment to key
satellite and constellation parameters
– Can we use this information to design and build better constellations?
• Here, we just focus on the simulation objectives and the baseline
parameters and assumptions
• The results from this study will be included in the next lecture
Space Environment – Space Debris (Vol. 3)

3. Space debris Space Environment – Space Debris (Vol. 3)
• The space debris environment: update
• Space surveillance/measurement of space debris
• Impacts on space operations
• Modelling of space debris
• Environment/evolutionary modelling
• Impact modelling
• Breakup modelling
• Re-entry modelling
• On-ground risk modelling
• Clean Space
Volume 3 (Week 7)

4. Why use a constellation? Space Environment – Space Debris (Vol. 3)
(From SESA3041/6079)
Typical drivers for constellations:
Global coverage
Temporal coverage
In combination with other requirements, e.g.:
High spatial resolution
Low latency
User experience
E.g. In communications missions, trend is towards low
orbit constellation systems principally because of the low
power requirement of the user terminal (a hand-held
phone has an isotropic, low radiated power transmitter for
physiological reasons)

5. Latency Space Environment – Space Debris (Vol. 3)
(From SESA3041/6079)
Latency for difference communications orbits:
E.g. SpaceX Starlink & OneWeb constellations
 latency is close to fibre-optic
Orbit Altitude Latency (one-
way/hop)
Latency (four-
way/full-hop)
LEO 1000 km 0.003 s 0.013 s
MEO 16000 km 0.053 s 0.213 s
GEO 36000 km 0.12 s 0.48 s

6. Starlink, OneWeb and Kuiper in LEO Space Environment – Space Debris (Vol. 3)
(Updated from SESA3041/6079)
OneWeb
Starlink
Kuiper

7. Starlink Space Environment – Space Debris (Vol. 3)
Data from SOCRATES (note that these are predictions for a 7-day period)
• Proportion of all
conjunctions in the
SOCRATES report
(excluding Starlink-on-
Starlink):
• ~11% of all
conjunctions < 5 km
(1-in-9) and ~9% of all
conjunctions < 1 km
(1-in-11)
• Also ~ 11% of
conjunctions< 1 km
affecting ACTIVE
spacecraft

8. A study for ESA Space Environment – Space Debris (Vol. 3)
• Cohen et al. 2016*:
• “A positive and creative vision for sustainability focuses on building something new
and clean rather than defeating something old and dirty.”
*Cohen, S.A., DeFrancia, K.L., and Martinez, H.J., 2016, J Environ. Stud. Sci., 6, 231-238, DOI: 10.1007/s13412-016-0368-7

9. A study for ESA Space Environment – Space Debris (Vol. 3)
• Review historical and proposed future
small satellite activities and
associated technologies;
• Perform long-term projections using
three evolutionary codes; and
• Conduct a detailed analysis of the
results of the first two activities, to
understand the sensitivity of the
debris environment to key satellite
and constellation parameters.
Results from the simulations were presented
@IAC in 2016 and at the European Conference
on Space Debris in 2017

10. Space Environment – Space Debris (Vol. 3)
Debris models
Three evolutionary debris models:
• DAMAGE (University of Southampton)
• LUCA (Technische Universität Braunschweig)
• SDM (IFAC-CNR)
All evolutionary models:
• Have full 3D capability
• Use the NASA breakup model (different implementations)
• Have different orbital propagators and collision prediction
algorithms
• Have been cross-validated (in previous IADC/ESA studies)
– LUCA was an exception

11. Space Environment – Space Debris (Vol. 3)
Reference case
• Initial population: all objects ≥ 10 cm
with perigee < 2000 km in orbit on 1 Jan
2013 (data from MASTER)
• Future launch traffic: repeat 2005-2012
launch cycle (data from MASTER)
• Projection period: 1 Jan 2013 to 1 Jan 2213
• Post-mission disposal (PMD) of 90%
of spacecraft and rocket bodies to a 25-
year orbit
• No explosions
• 50 Monte Carlo runs

12. Space Environment – Space Debris (Vol. 3)
Baseline constellation case
• Reference case for background traffic
• Walker-delta constellation comprising 1080
satellites in 20 orbital planes at 1100 km
altitude and inclined at 85°
• Satellite design lifetime of 5 years, 200 kg and
1 sq. metre
• Build-up phase from 1 Jan 2018 to 1 Jan 2021
• Replenishment phase from 1 Jan 2021 to 1 Jan
2070 (50 years)
• PMD of 90% of constellation spacecraft
to a 400 × 1100 km orbit
• Immediate de-orbit of rocket bodies
used to launch constellation
• No explosions in constellation

13. Overview of lecture 32
• In this lecture we looked back to previous lectures to remind ourselves why
constellations of satellites in LEO are useful and why they might present
problems for the space environment
• We then focused on a simulation study conducted for ESA:
– Aiming to understand the sensitivity of the debris environment to key
satellite and constellation parameters and to determine whether we can
use this information to design and build better constellations
• The results from this study will be included in the next lecture
Space Environment – Space Debris (Vol. 3)

14. Activities
• Revisit SESA3041/6079 lectures on
orbit design/constellations:
– Design drivers (especially latency)
– Constellation designs (e.g. Walker-
Star v Walker-Delta)
– Constellation maintenance (e.g.
Iridium)
– Constellation disposal (e.g. Iridium v
Globalstar)
• The ESA simulation study is reported in
a paper that is available to you on the
Blackboard site. You can read to gain a
further insight into the work
Space Environment – Space Debris (Vol. 3)